1. Field of the Invention
The present invention relates generally to telecommunications systems and methods for implementing Global Positioning System (GPS) receivers within mobile terminals, and specifically to provisioning GPS assistance information to GPS receivers within or attached to mobile terminals.
2. Background and Objects of the Present Invention
Cellular telecommunications is one of the fastest growing and most demanding telecommunications applications ever. Today it represents a large and continuously increasing percentage of all new telephone subscriptions around the world. A standardization group, European Telecommunications Standards Institute (ETSI), was established in 1982 to formulate the specifications for the Global System for Mobile Communication (GSM) digital mobile cellular radio system.
With reference now to FIG. 1 of the drawings, there is illustrated a GSM Public Land Mobile Network (PLMN), such as cellular network 10, which in turn is composed of a plurality of areas 12, each with a Mobile Switching Center (MSC) 14 and an integrated Visitor Location Register (VLR) 16 therein. The MSC/VLR areas 12, in turn, include a plurality of Location Areas (LA) 18, which are defined as that part of a given MSC/VLR area 12 in which a mobile station (MS) (terminal) 20 may move freely without having to send update location information to the MSC/VLR area 12 that controls the LA 18. Each Location Area 18 is divided into a number of cells 22. Mobile Station (MS) 20 is the physical equipment, e.g., a car phone or other portable phone, used by mobile subscribers to communicate with the cellular network 10, each other, and users outside the subscribed network, both wireline and wireless.
The MSC 14 is in communication with at least one Base Station Controller (BSC) 23, which, in turn, is in contact with at least one Base Transceiver Station (BTS) 24. The BTS is the physical equipment, illustrated for simplicity as a radio tower, that provides radio coverage to the cell 22 for which it is responsible. It should be understood that the BSC 23 may be connected to several BTS""s 24, and may be implemented as a stand-alone node or integrated with the MSC 14. In either event, the BSC 23 and BTS 24 components, as a whole, are generally referred to as a Base Station System (BSS) 25.
With further reference to FIG. 1, the PLMN Service Area or cellular network 10 includes a Home Location Register (HLR) 26, which is a database maintaining all subscriber information, e.g., user profiles, current location information, International Mobile Subscriber Identity (IMSI) numbers, and other administrative information, for subscribers registered within that PLMN 10. The HLR 26 may be co-located with a given MSC 14, integrated with the MSC 14, or alternatively can service multiple MSCs 14, the latter of which is illustrated in FIG. 1.
The VLR 16 is a database containing information about all of the MS""s 20 currently located within the MSC/VLR area 12. If an MS 20 roams into a new MSC/VLR area 12, the VLR 16 connected to that MSC 14 requests data about that MS 20 from the HLR database 26 (simultaneously informing the HLR 26 about the current location of the MS 20). Accordingly, if the user of the MS 20 then wants to make a call, the local VLR 16 will have the requisite identification information without having to reinterrogate the HLR 26. In the aforedescribed manner, the VLR and HLR databases 16 and 26, respectively, contain various subscriber information associated with a given MS 20.
Determining the geographical position of a MS 20 within a cellular network 10 has recently become important for a wide range of applications. For example, positioning services may be used by transport and taxi companies to determine the location of their vehicles. In addition, for emergency calls, e.g., 911 calls, the exact location of the mobile terminal 20 may be extremely important to the outcome of the emergency situation. Furthermore, positioning services can be used to determine the location of a stolen car, for the detection of home zone calls, which are charged at a lower rate, for the detection of hot spots for micro cells, or for the subscriber to determine, for example, the nearest gas station, restaurant, or hospital, e.g., Where am I service.
One known solution of locating an object is the Global Positioning System (GPS). GPS is a well-known technology used by many military and civilian applications. It is based upon a constellation of satellites launched by the U.S. government beginning in 1978. The GPS satellites transmit the standard positioning service (SPS) signal, which is available for civilian applications, on a 1575.42 MegaHertz carrier. Each satellite uses a unique 1023-chip Gold code at a rate of 1.023 MegaHertz, such that all codes repeat at 1 millisecond intervals.
Each satellite also transmits a unique 50 bit/second navigation message containing parameters that allow GPS receivers on earth to compute a precise position solution. The navigation message includes a precise time reference as well as parameters that precisely describe the orbital positions and clock corrections for the satellites. In general, GPS receivers compute a position solution by searching for all visible satellites, which can be accomplished by correlating the received signal with replicas of the respective Gold codes, demodulating the navigation message of each visible satellite to obtain a time reference and orbital position, computing a range estimate for each visible satellite that includes the GPS receiver clock uncertainty, and, if at least four satellites are visible, computing the GPS receiver position and clock correction using the range estimate.
The duration of the GPS positioning process is directly dependent upon how much information the GPS receiver has. Most GPS receivers are programmed with almanac data, which coarsely describes the satellite positions for one year. However, if the GPS receiver does not have some knowledge of its own approximate location, then the GPS receiver cannot correlate signals from the visible satellites quickly, and therefore, cannot calculate its position quickly. Thus, in order to implement a GPS receiver effectively within a mobile terminal 20, in order to meet demands for expedited and accurate positioning, e.g., FCC phase II E-911 service, there must be some way to provide this type of accurate assistance data, e.g., local time and position estimates and satellite ephemeris and clock information, which varies according to the MS 20 location, to the GPS receiver within or attached to the MS 20 quickly.
It is, therefore, an object of the present invention to send the necessary assistance GPS information over the existing wireless network to the GPS receiver within the mobile terminal.
The present invention is directed to telecommunications systems and methods for provisioning assistance Global Position System (GPS) data to a GPS receiver within a mobile terminal. This can be accomplished by having multiple reference GPS receivers located throughout the cellular network, each reference GPS receiver being capable of providing locally valid lists of visible satellites and the associated ephemeris and clock correction information. This data from each reference GPS receiver is valid for a radius of up to 300 kilometers around the reference GPS receiver site. However, if a differential GPS solution is utilized, the data for the GPS receiver is only valid for a radius of up to 50 kilometers. The location of the Base Transceiver Station within the cell that the mobile terminal with a built-in GPS receiver is currently located in can be used as the local position estimate for that mobile terminal. From this local position estimate, the nearest reference GPS receiver can be ascertained and the relevant assistance data can then be sent to the GPS receiver within the mobile terminal through the cellular network to enable the built-in GPS receiver to calculate its position relatively quickly. Advantageously, compared with previous solutions, the accuracy of the position of the mobile terminal using a GPS receiver can be reduced to a 5 meter radius (using differential correction information), instead of a cell radius (500 meters to 35 kilometers) or a location area radius, as in previous solutions.